This invention relates to the recycling of a chopped strand mat, and in particular, to the recycling and shredding of an edge portion of a chopped strand mat. More particularly, this invention relates to an apparatus for and method of shredding an edge portion of a chopped strand mat so that the individual strands in the edge portion may be recycled in the chopped strand mat manufacturing process. The invention can be useful in the manufacture of chopped strand mats that may be used as reinforcement in plastic or composite products by eliminating a waste stream in the manufacturing process.
Chopped strand mats, formed from glass fibers or other mineral strands, are commonly used as reinforcement in plastic or composite products. A chopped strand mat is typically made up of randomly oriented chopped glass fiber strands that are bonded together with a thermoplastic or thermoset resin. A chopped strand mat may be laminated or impregnated with resin and subsequently molded to form a variety of articles such as boat hulls and vehicle parts.
There are numerous ways to manufacture chopped strand mats. An example of a known chopped strand mat forming apparatus and method is disclosed in U.S. Pat. No. 2,719,336 to Stotler (xe2x80x9cStotlerxe2x80x9d), the disclosure of which is expressly incorporated herein by reference. Conventional manufacturing processes involve the formation of the mat and the takeup of the finished mat on a roller or reel.
Chopped strand mats are initially formed with a width greater than the desired finished width. The edges of the mat are then trimmed to remove the non-uniform edge portions and produce the desired finished width. The trimmed portions are typically discarded as unusable. This produces waste that must be disposed of and incurs cost in wasted raw materials.
An example of an apparatus for and method of reclaiming fiber reinforcement from a composite product is shown in U.S. Pat. No. 5,312,052 to Dellekamp (xe2x80x9cDellekampxe2x80x9d). Dellekamp discloses a fiber reclaimer that separates glass fibers from resin in a fiber reinforced plastic waste product. The plastic waste product is sheared and crushed in a roller mill to break the bond between the fiber reinforcement and the plastic resin.
As shown in FIG. 2 of Dellekamp, the roller mill 17 includes rollers 18 in pairs 20, 21, and 22. Each pair of rollers includes different sized serrations 28 to crush and separate the plastic waste product passing between them. Further, each pair of rollers is spaced apart to form a gap 19 between the respective roller surfaces for passage of the waste product therethrough. Each of the gaps 19 between the rollers is vertically aligned and decreases in size for each successive roller pair. Each roller pair 20-22 includes a pair of springs 24-26 that allows the rollers to move laterally away from one another to permit oversized material to pass through the gaps 19.
In Dellekamp, each of the rollers in a pair is driven at different speeds to produce an abrading action on the plastic waste product between them. The downstream rollers are driven at higher speeds than the upstream rollers to enable the volume of material that passed through a wider gap between upstream rollers to pass through the smaller gap between the downstream rollers.
Dellekamp""s method and apparatus are not suitable for reclamation of edge trim from chopped strand mat.
The shortcomings of the prior art are overcome by the disclosed apparatus for and method of recycling the edge portion of a chopped strand mat. The method includes the steps of trimming an edge portion of the chopped strand mat, transporting the edge portion to a shredder assembly, and shredding the edge portion into individual strands or filaments. The separated strands are introduced with new chopped strands into the chopped strand mat forming process.
The apparatus for recycling the edge portion of the mat includes a shredder assembly for separating the edge portion into individual strands. The shredder assembly includes two pairs of rollers that engage the trimmed edge portion. The first and second pairs of rollers are driven at first and second rotational speeds, respectively. Preferably, the second speed is greater than the first speed. The mat is pinched between each pair of rollers and is thereby placed under tension due to the different rotational speeds. The tension applied to the mat breaks the resin bond between the strands in the mat, separating the mat into individual strands on the downstream side of the second pair of rollers. The individual strands are then transported to a forming hood of the chopped strand mat forming apparatus and introduced into the chopped strand mat manufacturing process.